How to select the surface treatment process of HASL, ENIG and OSP circuit boards?

After designing the PCB, we need to select the surface treatment process of the circuit board. Now the commonly used surface treatment processes of the circuit board include HASL (surface tin spraying process), ENIG (gold deposition process) and OSP (anti-oxidation process). How should we choose the commonly used surface treatment process? Different PCB surface treatment processes have different charges and different final effects. You can choose according to the actual situation. Let me tell you the advantages and disadvantages of three different surface treatment processes: HASL, ENIG and OSP.
1. HASL (surface tin spraying process)
Tin spraying process is divided into lead tin spraying and lead-free tin spraying. Tin spraying process was once the most important surface treatment process in the 1980s, but now fewer and fewer circuit boards choose tin spraying process, because the circuit boards are developing towards "small and fine". Tin spraying process will lead to poor production caused by tin beads and spherical tin dots during the welding of fine components, Pcba# processing plants often choose ENIG and SOP surface treatment processes in order to pursue higher process standards and production quality.
Advantages of lead tin spraying: low price, excellent welding performance, better mechanical strength and gloss than lead tin spraying.
Disadvantages of lead tin spraying: lead tin spraying contains lead heavy metals, which is not environmentally friendly and cannot pass RoHS and other environmental protection evaluation.
Advantages of lead-free tin spraying: low price, excellent welding performance, relatively environmental protection, and can pass RoHS and other environmental protection evaluation.
Disadvantages of lead-free tin spraying: mechanical strength and gloss are not as good as lead-free tin spraying.
The common disadvantage of HASL: it is not suitable for welding pins with fine gap and too small components, because the surface flatness of tin spray plate is poor. It is easy to produce tin beads in PCBA processing, which is easy to cause short circuit to fine gap pin components.
2. ENIG (gold precipitation process)
Gold deposition process is a relatively advanced surface treatment process, which is mainly used on circuit boards with connection functional requirements and long storage life.
ENIG's advantages: it is not easy to oxidize, can be stored for a long time, and the surface is flat. It is suitable for welding fine gap pins and components with small solder joints. Reflow soldering can be repeated many times without reducing its solderability. It can be used as the substrate of cob wiring.
Disadvantages of ENIG: high cost and poor welding strength. Because the electroless nickel plating process is used, it is easy to have the problem of black disk. The nickel layer will oxidize over time, and long-term reliability is a problem.
3. OSP (anti oxidation process)
OSP is an organic film formed chemically on the surface of bare copper. The film has oxidation resistance, heat shock resistance and moisture resistance to protect the copper surface from further rusting (oxidation or vulcanization, etc.) in the normal environment; It is equivalent to an anti-oxidation treatment, but in the subsequent welding high temperature, the protective film must be easily and quickly removed by the flux, and the exposed clean copper surface can be immediately combined with the molten solder to form a solid solder joint in a very short time. At present, the proportion of circuit boards using OSP surface treatment process has increased significantly, because this process is suitable for circuit boards with low process and high process. If there are no functional requirements for surface connection or storage period, OSP process will be the most ideal surface treatment process.
Advantages of OSP: it has all the advantages of bare copper plate welding. Overdue (three months) plates can also be re treated, but usually only once.
Disadvantages of OSP: it is easy to be affected by acid and humidity. When used in secondary reflow soldering, it needs to be completed within a certain time. Generally, the effect of secondary reflow soldering is poor. If the storage time exceeds three months, the surface must be treated again. It shall be used up within 24 hours after unpacking. OSP is an insulating layer, so the test point must be printed with solder paste to remove the original OSP layer before contacting the pin point for electrical test. The assembly process needs to be greatly changed. If the unprocessed copper surface is detected, it will be detrimental to ICT, and the too sharp ICT probe may damage the PCB. Manual preventive treatment is required to limit ICT testing and reduce the repeatability of testing.
The above is the analysis of the surface treatment process of HASL, ENIG and OSP circuit boards. You can choose which surface treatment process according to the actual use of circuit boards.

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Keyword：HASL   ENIG   OSP circuit board   Surface treatment process   Surface tinning process   Immersion gold process   Anti-oxidation process   Commax-Tech Electronic